Basis of Presentation and Significant Accounting Policies (Schedule of Net Operating Revenue) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues	$ 3,453	$ 3,451	$ 3,562	$ 3,689	$ 3,059	$ 3,666	$ 4,144	$ 4,486	$ 14,155	$ 15,353	$ 18,438
Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues									14,155
Prior to Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues										18,398	21,275
Medicare [Member] | Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues									3,730
Medicare [Member] | Prior to Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues										4,188	5,089
Medicaid [Member] | Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues									1,876
Medicaid [Member] | Prior to Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues										1,900	2,234
Managed Care And Other Third Party Payors [Member] | Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues									8,349
Managed Care And Other Third Party Payors [Member] | Prior to Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues										9,991	11,354
Self-Pay [Member] | Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues									$ 200
Self-Pay [Member] | Prior to Adoption of ASC 606 [Member]
Health Care Organization, Receivable and Revenue Disclosures [Line Items]
Net operating revenues										$ 2,319	$ 2,598